1. Field of the Invention
The present invention relates to an apparatus for and a method of monitoring the build-up of ice on engine and plant parts. It is generally known that the build-up of ice on the surface of exposed engine and plant parts must be monitored to avoid damages resulting from this ice build-up by an early detection of same. A build-up of ice at the intake of the axial compressor of gas turbines or aircraft jet engines which may be produced, for instance, due to changes of the temperature or--at low temperatures--due to a change of the humidity of the air is specifically dangerous because the forming of ice changes the blade profile which leads to a discontinuity of the air- or gas flow, respectively, as well as of the pressure along the axial extent of the compressor which may lead to a reduced infeed of air or even to a total failing of infed air. Such condition results in the already compressed air present in the engine parts behind the compressor to stream suddenly back towards the compressor intake whereby pressure waves or compressional waves, respectively, are generated, which, as is generally known, can lead to a destruction of the blades.
2. Description of the Prior Art
A known apparatus for monitoring the build-up of ice comprises a plug projecting radially into the intake of a compressor, which plug is made to oscillate by an electric means whereby the frequency of the oscillation of this plug changes in accordance with deposits on its surface, which deposits may, for instance, be ice. This change of the frequency is used as measured value regarding the detection of deposits on this plug or on the engine parts and plant parts, respectively, adjacent to this plug.
This monitoring apparatus or device, respectively, features, however, the drawback that it can be used only if the ambient air is clean, i.e. it can be used, for instance, only for aircraft jet engines operating at great heights. If such monitoring apparatuses are used at the ground surface in areas of highly contaminated air such, for instance, in gas turbines installed in power plants, the deposits of such contaminants on the plug change its frequency of vibration or oscillation, respectively, such that erroneous monitoring signals are produced.